Drive shaft with non-cylindrical shape

ABSTRACT

A drive shaft body extends between axial ends and has an outer peripheral surface with undulations extending between relatively greater and smaller outer diameters. The undulations extend along a non-zero angle relative to a circumferential direction defined relative to a drive axis of the drive shaft. The undulations extend along a spiral. The drive shaft body is formed of a fiber-reinforced composite material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/807,051 filed on Feb. 18, 2019.

BACKGROUND

This application relates to drive shafts having non-cylindrical shapes.

Drive shafts are known and utilized to connect any number of drivencomponents to drive inputs. One known application is to drive propellersfor an aerospace application.

Historically, drive shafts have had a cylindrical tubular portion withconstant cross-section along the shaft length extending betweendiaphragms at each end. The diaphragms allow flexibility under bendingand axial load, as the drive axes and positions between the drive inputand the driven component may change.

SUMMARY

A drive shaft body extends between axial ends and has an outerperipheral surface with undulations extending between relatively greaterand smaller outer diameters. The undulations extend along a non-zeroangle relative to a circumferential direction defined relative to adrive axis of the drive shaft. The undulations extend along a spiral.The drive shaft body is formed of a fiber-reinforced composite material.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment.

FIG. 2 shows an alternative embodiment.

FIG. 3A shows yet another embodiment.

FIG. 3B shows an embodiment.

FIG. 4A shows yet another embodiment.

FIG. 4B shows another embodiment.

FIG. 4C shows another embodiment.

FIG. 5A shows a distinct embodiment.

FIG. 5B shows a variation on the FIG. 5A embodiment.

FIG. 5C shows yet another variation on the FIG. 5A embodiment.

FIG. 5D shows another variation

DETAILED DESCRIPTION

A drive assembly 20 is illustrated in FIG. 1 as an axial cross-sectionalview for connecting a drive input 22 to a component to be driven 26. Thecomponent to be driven 26 may be a propeller such as on a helicopter.However, the teachings of this disclosure extend to other driveapplications.

Under some conditions, the input axis from the drive input 22 and theaxis to the component 26 may shift, thus, an intermediate drive shaft 24of length L desirably accommodates the shifting. The drive shaft 24 hasan outer peripheral surface 25 and inner peripheral surface 27 extendingbetween axial ends 30 and 31. As shown, a diameter of the drive shaft 24changes in a continuous manner between the ends 30 and 31 in the FIG. 1embodiment. It could be said that the diameter changes through aninfinite number of diameters between the ends 30 and 31.

As shown, a first smaller diameter d₁ may be found at the end 30, withan intermediate increasing diameter d₂, and a largest diameter d₃ withina middle part of the drive shaft illustrated by central point 32. Ofcourse mid-points other than the center can be used. The outer periphery25 then returns to smaller diameters, again through an infinitelyvarying range of diameters until it reaches the opposed end 31. Asimilar definition of variable diameters applies along the innerperiphery 27. A design such as shown in FIG. 1 (or FIG. 2) may beespecially helpful in optimization of parameters of dynamic behavior ofthe shaft, such as, for example, frequencies of free vibrations.

FIG. 2 shows an axial cross-sectional view of a distinct embodimentwherein a drive shaft 40 extends between axial ends 42 and 44. There isa larger diameter d₄ at the ends 42/44 and a smaller diameter d₅ withina middle part of the drive shaft here the center 46. Again, middlepoints other than the center can be used. Here again, the diameterschange through an infinite number of diameters between the ends 42 and44. Here again, these changes occur along the outer periphery 19 and/orinner periphery 17

The description of changing through an infinite number of diameters isto distinguish drive shafts having distinct radially outwardly extendingrings, as an example. The limitation “infinite number of diameters”should be interpreted with the analysis of a curve under calculus inmind, i.e., with definition of shaft outer or inner shape as continuousvariation of diameter as a function of the shaft axial position. It doesnot imply any particular length of curve other than as may otherwise bementioned in this document.

FIG. 3A shows an axial cross-sectional view of an embodiment 60 whereinthere are two increasing diameter portions or subsections 64. Here,there is a diameter d₆ at the end 62, an enlarged diameter portion d₇ atintermediate portions 69 of each of the subsection 64, and anothersmaller diameter d₈ at a central portion 66. Other embodiments of thedesign shown in FIG. 3A may include more than two increasing diameterportions along the shaft length. Such embodiments may have, for example,three or four portions with increasing diameter. FIG. 3B shows amodification from the FIG. 3A structure. In FIG. 3B, shown as an axialcross-sectional view, a drive shaft embodiment 160 has two portions 162similar to the portion 64 of FIG. 3A with a central portion 164 which isgenerally cylindrical. As shown, the portions 162 each extend for onethird of the overall length L of the drive shaft 160 measured betweenends 165.

The embodiments shown in FIGS. 1-3 could be said to include a driveshaft having an outer diameter measured about a rotational axis z thatchanges through a portion of an axial length between ends of the driveshafts and through an infinite number of diameters through a portionextending across at least 15% of the axial length. More narrowly, theinfinite number of diameters occurs across at least 33% of the axiallength. The axial length is illustrated as L in FIGS. 1-3. Of course, inFIGS. 1, 2 and 3A, the infinite variation in diameters occurs across theentire length L whereas in the FIG. 3B embodiment, it only occurs whenlengths L₁ or L₃ are, at least, 15%, or, more narrowly, at least 33% ofthe entire length L.

FIG. 4A shows an axial cross-sectional view of yet another embodiment 80wherein the drive shaft extends between axial ends 82 and it has anouter peripheral surface 84. Local undulations in the radial direction86 are formed in the outer peripheral portion 84. This provides anopportunity to enhance bending flexibility while maintaining hightorsional stiffness.

The undulations 86 still results in the infinite variation of the outerdiameter. Designs shown in FIGS. 1 and 2 are convex or concave,respectively, in the axial cross-sectional view. Similarly, each portion64 in the design shown in FIG. 3A or each portion 162 shown in FIG. 3Bare convex as well.

The term “convex” means that an axial cross-section shape extends alonga curve to greater diameters to a mid-point, and then extends along acurve to smaller diameters. That is, it is bowed outwardly. The term“concave” means the opposite, and is bowed inwardly.

In contrast with these designs, introduction of local undulations makestheir shapes distinguishly non-convex (or non-concave) within eachportion of the shaft with variable diameter. Still, as shown in FIG. 4A,if centers U_(c) of local undulations 86 are connected, they maygenerate either convex or concave shapes in the axial cross-sectionalview.

These local undulations can be uniform or non-uniform along the shaftlength. In other embodiments, the local undulations may be partiallyapplied along the shaft length.

FIG. 4B shows an embodiment 80B extending between ends 82B. Localundulations 86B are formed within the outer surface 84B, and inlocations adjacent the ends. There is a central location 500B withoutthe undulations.

FIG. 4C shows an embodiment 80C having ends 82C. Localized undulations86C are formed in the outer periphery 84C, and at a central area.Portions 500C without undulations are formed on each axial end of thecentral section.

All of the embodiments shown in FIGS. 1, 2, 3A, 3B and 4A-C (and FIG. 5Das will be disclosed below) could be said to have an effective shapethat is either convex or concave along at least 15% of an axial lengthof the drive shaft. In embodiments the convex or concave shape extendsacross at least 33% of the axial length, and in at least one embodiment100% of the axial length. The term “effective axial cross-sectionalshape takes into account the feature with regard to the centers U_(c) ofthe undulations along with the general shape of the drive shaft.

Similar variations with local undulations could be made to theembodiments shown in FIG. 2 or 3A and 3B.

FIG. 5A shows yet another drive shaft embodiment 100. Drive shaftembodiment 100 has local spiral undulations 102, which extend at anon-zero angle relative to a hoop or circumferential direction about acentral axis 104. As can be seen in the embodiment 100, the undulationsextend entirely between the ends 106 and 104. FIG. 5B shows a driveshaft embodiment 110 extending between ends 112. There are spiralundulations 114 adjacent each of the ends 112 with a central area 116without undulations.

FIG. 5C shows yet another embodiment 120 extending between axial ends122. Here, there are areas 124 adjacent each end 122 without undulationsand then a central area with undulations 126, again being spiral.

Similar variations with local spiral undulations could be made to theembodiments shown in FIGS. 1, 2, 3A and 3B.

FIG. 5D shows an example 150 wherein spiral undulations 154 formedextending along an otherwise convex or concave shape betweendown-selected ends 152 of a representative shaft segment. It should beunderstood that such a shape could extend along the entire length of thedrive shaft, or portions as otherwise disclosed in this application.

The several disclosures in this application provide a designer with apowerful ability to design a drive shaft for a specific challenge. Thedrive shafts of this disclosure may be formed of fiber-reinforcedcomposite material or metals. In case of composite material, thermos-setor thermoplastic resins may be used, while fiber reinforcement may beperformed by carbon fibers, glass fibers, organic fibers or theircombinations. In case of metallic shafts, aluminum, titanium, steel maybe used for example. By carefully designing the cross-sectional shape ofthe shaft as a function of shaft length, additional design parameterscan be optimized to achieve desired structural performance for specificload scenarios, or to satisfy contradictory trends such as, for example,a high torsional stiffness with a relatively high bending flexibility,or to satisfy challenges of excessive vibrations of relatively thin-walllightweight designs.

A drive shaft under this disclosure could be said to have a drive shaftextending between axial ends and having at least one portion throughwhich an outer diameter of the drive shaft changes through an infinitenumber of diameters. The at least one portion extends across at least15% of an axial distance between the axial ends of the drive shaft.

A drive shaft under this disclosure could be said to have a drive shaftextending between axial ends and having an outer peripheral surface withundulations extending between relatively greater and smaller outerdiameters. The undulations extend along a non-zero angle relative to acircumferential direction defined relative to a drive axis of the driveshaft.

A drive shaft under this disclosure could be said to have a drive shaftextending between axial ends and having at least one portion having aneffective axial cross-sectional shape which is either convex or concave,across at least 15% of an axial distance between said axial ends of saiddrive shaft.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this disclosure. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this disclosure.

The invention claimed is:
 1. A drive shaft comprising: a drive shaftbody extending between axial ends and having an outer peripheral surfacewith undulations extending between relatively greater and smaller outerdiameters, with said undulations extending along a non-zero anglerelative to a circumferential direction defined relative to a drive axisof said drive shaft such that said undulations extend along a spiral;and said drive shaft body being formed of a fiber-reinforced compositematerial.
 2. The drive shaft as set forth in claim 1, wherein there isat least one axial extent of said drive shaft which does not have saidundulations.
 3. The drive shaft as set forth in claim 2, wherein saidextent without said undulations is between said axial ends and therebeing an extent with said undulations between said extent without saidundulations, and at least one of said axial ends.
 4. The drive shaft asset forth in claim 2, wherein there are extents with said undulations oneach axial side of said extent without said undulations.
 5. The driveshaft as set forth in claim 1, wherein one end of the drive shaft bodyis fixed to a source of drive and a second end is fixed to drive acomponent.
 6. The drive shaft as set forth in claim 5, wherein thecomponent is a propeller.